Safety control system for gas burners



April 13, 1954 R. SHOTTENFELD SAFETY CONTROL SYSTEM FOR GAS BURNER-S 3Sheets-Sheet 1 Filed May 18, 1951 INVENITOR Ri yard Sh offenfe/ ESQATTORNEY Apr 9 4 R. SHOTTENFELD v 2,675,069

SAFETY CONTROL SYSTEM FOR GAS BURNERS Filed May 18, 1951 3 Sheets-Sheet2 Fig. 2 l L- m f l FHA;

ATTOR EY Patented Apr. 13, 1954 UNITED STATES PATENT OFFICE SAFETYCONTROL SYSTEM FOR GAS BURNERS Richard Shottenfeld, Jamaica, N. Y.,assignor to EnsignRibbcn lsurners lnc Pelham Manor, N. Y., a corporationof New York Application May 18, 1951, Serial No. 226,965

2 Claims.

in safety devices or safety control systems for automatically shuttingoff the gas supply to the burnerin case of failure of the ignitionspark.

Automatic safety devices or safety control systems are known forshutting off the gas case ofspark failure such as caused by failure ofthe power supply or b a variety of faults that may develop in theignition ystem itself.

Such ignition systems usually employ an ignition transformer capable ofproducing an output voltage'of the order of 5000 volts across the opencircuited secondary which voltage is provided for insuring the spark tobreak down the air gap between the spark electrodes. Such ignitiontrans-- formers are designed to deliver an output or secondary currentthat is never in excess of a desired limit value, for instance of theorder of 15 milliamperes. In thisway the transformer secondary currentis never allowed to exceed a desired predetermined safe valueirrespective of the load across the secondary. This mean that thecurrent is self-limiting and maintain itself substantially at thepredetermined value.

Because of the high value of the voltage needed for operating the sparkin such devices it is inadvisable to utilize voltage as a criterion ofspark operation, from which to derive the desired gas valve control, andit is preferable to utilize as the operating criterion the secondarycurrent flowing through the spark circuit. Thus a voltage-operatedcontrol system is to be distinguished from a current-operated system.

However, it is becauseof the aforementioned self-limitingcharacteristics of the transformer current that the current-operateddevices lack the ability to distinguish beween a current that isspark-producing and a currentpassing through the electrodes when thereis no spark as in the case of short circuiting ofthe electrodes.

Thereforeitisa problemin. suchknown current-operated devicesithat, whileeffective in case of systemic or other faults, they will fail to shutsoff the gas supply when the fault is due to short circuiting of theelectrodes for example by a metal particle accidentally bridging the airgap between the electrodes when current may con it tinue to pass throughthe eleotrodeseven though producing no spark.

t is an object of this inventionto provide an... improved safety controldevice or system which: even though current-operated, provides addedsafety by effecting gas shut off automatically in case ofshort-circuiting of the spark electrodes; and, more particularly toprovide such a control system that of itself is simpleand relativelyinexpensive to produce, as well as simple and inexpensive to maintain,and which is capable of being operated from a single relay power sourcein a manner which provides a high degree of a safety with respect toother components of. the systen1,.in that it will cause the gas valve toclose inthe event of failure of such a component.

This object is attained by utilizing as a criteri-i on of sparkoperation for gas valve control, certain differences in thecharacteristics. or wave form of the secondary alternating current when.

the spark functions normally, and the character. istics or wave form ofthe secondary current when no sparkis maintained as when the spark gapis shorted, that is by utilizing such diifer ence of the waveforms toeifectga shut-off as l and when the current changes fronrone Wave formto the other. The wave form of the current in case of short circuit. ofthe. spark gap is that current shortly after the beginningof each halfwave and a rapid decrease shortly before the end of .each half wave. Inthisway there appears between each 'such rapid decreaseand increase an.

interruption of the spark-producing current. In

other words, there occurs an abnormally rapid decrease in the magnitudeof the current before, and-an abnormally rapidincrease in the magnitudeof the current after each interruptionas distinct from the smoothuninterrupted transitions from'one halrwave to the next of thefamiliarsmooth sinusoidal wave form of an alternating current. These rapidincreases and decreases in the magnitude of the spark-producing currentconstitute high frequency components thereof.

These characteristics of the interrupted wave form are due to the factthat for a short period of time before and after the instant ofzerosecondary-voltage that voltage is insuificient to break down the airgap between the elecrodes. That is to say, during each half cycle thesecondary voltage must first build up to a critical value in order thatthe spark may start, where as the spark stops when the voltage fallsbelow a critical value. Consequently, there is one starting and onestopping of the spark during each half cycle of the secondary voltagewave. In this way, as the spark establishes itself across the air gap,the secondary current rises almost instantaneously from zero to near themaximum limit value permitted by the transformer itself. and converselyas the spark stops the current falls almost, instantaneously from nearthe maximum limit value to zero.

This invention provides gas valve controlling means which, while underthe influence of the characteristics of the current of interrupted waveform, keep the gas valve open concurrently with the normal functioningof the spark, but which controlling means close the gas valve inresponse to a change of current from the interrupted to thenon-interrupted wave form, which change is the criterion of sparkfailure utilized according to this invention for automatically effectingthe gas shut-ofi.

This invention provides a control system which responds to thecharacteristic rapid increases and decreases in the magnitude of thecurrent by maintaining the gas valve open while the ignition sparkoperates normally, and by closing the valve in the absence of such rapidincreases and decreases as due to a short circuit across the gap when nospark occurs even though a current of uninterrupted wave form is passingthrough the electrodes. In other Words, this control system keeps thegas valve open only as long as it is under the influence of the rapidincreases and decreases of the secondary spark producing current, butcauses the valve to close as soon as the current assumes a wave form inwhich these rapid current changes are lacking.-

Further particularized, this invention provides gas valve actuatingmeans responsive to the rapid changes in the magnitude of the currentand non-responsive to the relatively gradual sinusoidal cyclic changeswhich characterize the wave form when no sparking takes place. Suchselective responsiveness is attained by providing control means capableof deriving or abstracting energy only from a current of sufficientlyrapid change in magnitude such as the spark producing interruptedcurrent Wave form, and supplying that energy through relay means tocontrol the gas valve to hold it open, and to close the valve in theabsence of such energy. That is to say, the invention providesfrequency-discrimi 'nating circuit means associated with the sparkproducing circuit for selectively abstractingenergy from thehigh-frequency components of the spark producing current and adapted tosupply such energy for control purposes during the functioning of thespark.

According to one feature, a device within the control system forabstractin energy for valve control purposes comprises a resonantcircuit coupled with and under the influence of the spark producingcurrent.

A resonant circuit of itself is Well known, and it comprises aninductance and a capacitance so connected that when a current passingthrough the resonant circuit is changed abruptly in magnitude, then thevoltage across this circuit due to such abrupt change does not itselfchange abruptly but rather changes as an oscillatory function of timenamely as an exponentially damped sinusoidal wave.

Such abrupt change of current may be said to shock the resonant circuitinto oscillations at its resonant frequency comparable to a bell beingstruck into ringing or a resilient mechanical system being subjected toa sudden impact causing it to vibrate when the energy of the impact isabsorbed in and dissipated by the vibrations. Similarly, the electricalshock imparted to the resonant circuit by the rapid increase or decreaseof the current is absorbed in and dissipated by the subsequentoscillations of a resonant current and voltage resulting from the shockwithin that circuit. Hence the resonant circuit is said to ring (like abell) at its resonant frequency.

This frequency of resonance, according to this feature, is very muchhigher than the frequency of the power supply to the ignitiontransformer. For example, while the frequency of the power supply to theignition transformer may be 60 cycles per second, the frequency of theresonant circuit may be on the order of several million cycles persecond. Furthermore, this feature provides that the highest peak voltageappearing across the resonant circuit will be of the order of to 200volts, whereas the spark producing peak voltage may be of the order of7500 volts. Therefore the variations or oscillations in the voltage ofthe resonant circuit will have no appreciable efiect on the spark, eventhough they utilized according to this invention to provide energy forautomatically controlling the operation of the gas valve. On the otherhand,

when no spark is being produced because of short circuiting of theelectrodes, then the current that passes through the resonant circuit,because of its uninterrupted wave form, produces only a voltage that ispractically zero or negligibly small.

At any rate, during each ring of the resonant circuit the voltage acrossthat circuit varies as a function of time and follows the law of anexponentially damped sinusoidal wave which is an expression of the factthat the energy imparted to the resonant circuit by abrupt currentchange is being absorbed by and dissipated in the circuit losses. Thedamped sinusoidal wave represents What is herein termed a high frequencycomponent of the spark producing transformer secondary current which inturn possesses a relatively low frequency at relatively high voltage.

According to this invention, a portion of the energy in the ringingresonant circuit is utilized through relay means for controlling the gasvalve and to hold it open only during the normal functioning of thespark.

According to a feature, since the energy furnished by a single ring ofthe resonant circuit may be insufficient to operate directly a practicaltype of relay, provision is made for the relay to be actuated by theaccumulated en ergy of a sequence of such rings.

acumen According. to another; feature; -...the energy needed for.actuating the {gas valve-controlling. relay; means; is convertedfromrA.-.-G. formto...

D.-C. form.,and.as such is accumulated. in a condenser. In other: words,the aforementioned portion. of the energy in the resonantacircuit, :to

be utilizedfor controlling the gas valve, is transferred to and storedwithinthe condenser. is, the condenser, receiving increments of en.-

ergy with each ring of. the resonantcircuih: isenabled to hold a chargethus accumulated: by a one-way conductor such as a rectifier func-.

tionally interposed between the conde'nserand thelsource of energyasrepresented by the resonant circuit when in a state of ringing? Thusthe. condenser becomes gradually chargedto a. D.-C. voltagesubstantially equalto theahighest peak voltage attainedby the dampedsinus-. v oidal voltage. wave of the ringing. This D.-C."

voltageis utilized through the relay *action of a current amplifierelectronicstube to .holdthe gasyvalve open :while 'the. spark functions.normally..- That is, the:D.-C. voltage is impressed That.

uponathe input electrode or grid of the tube which in turn acts .inproportion to such impressed voltage to varythe flow of l. currentthrough the tube from an independent auxiliary power source employed foractuating the gas valve proper. That is, the D..-'C. voltagefrom thecondenser operates through the tube to hold the gas valve open only'aslong. as the condenser remains sufficiently charged, provision beingmade for the condenserwto discharge automatically andfor the D.-C.voltage to drop to zero within: a predetermined period of time, afterthe supplyof energy increments from the ringing. of the resonant circuitceases, due to spark failure. The amplifier tube circuit is designedtoshut. ofi theauxiliary powersupply when the D.-C; grid voltagedropssuificiently orbecomes zero to efiect. automatically the closing of athe gas valve. In'this Way cumulative energy of a sequence of dampedsinusoidal waves is uti lized to" control the desired functioning of thegas .valve..

Summarizing, the control systemcomprises fourtfunctional.operatingunits, namely, (a) a gas burner unit comprising a gasburner, a pair ofignition spark electrodes for the burner, a gas control .valve for theburner, and an electrically energized gas valve actuating device to holdthevalve open when energized and to close 7 it when deenergized; (b)anignition unit. comprising; an ignition transformer for supplying sparkcurrent to theelectrodes, and asparkwith. the transformerin such amanner as to abstract energy fromthespark producing current; (0)arrectifying energy-storing unit comprising a rectifier for changing theabstracted functioning normally.

In. terms -of. rcircuits z the: control. system race:

detecting resonant circuit functionally coupled condenser .soastoenergize the valve actuating means or solenoid coil only whilethespark is.

6 cording; tor this invention: presents. itself";v as follows:

The; ignition...transformer:secondary current 1 contains .high frequencycomponents only when; the ignitionspark is-v functioningibut; not whenw.the. spark istabsent due to theelectrodes having...

become: short circuited.

Inxconjunction with the ignition circuit .there are provided afrequencydiscriminating circuit means or agresonant: circuitwhich is frequency?discriminating...in that it. selectively. abstracts energy fromthehighufrequency component of] the spark producing. current, but remainsnon-..

responsive to... any ucurrent in which the high frequency components areabsent such; as curs rent; passing 1 through short' circuited. electrodes-- The abstracted energyis supplied .to a .rectifying energy.storing circuit where it is .accumulatedsup .tora predetermined voltage,from .which circuit. the accumulated energy 2 isautomaticallyadischarged whenever the sup;

ply xofrenergy; ceases. This predetermined voltJ-r agembeing: amanifestation; of the. storedxrena ergyis: utilized in and by a relaypower circuit... comprising an amplifier tube the .operationrofJ whichis governed by that voltage. That isgthe voltage is impressed upon-thegrid of thatwamplifier tube in such a manner. .thatithewtube acts topass current sufiicient to actuate the. valve operating means to..holdthe .valve open... as long as the energy supply and thereby'the.gridvoltage are .beingr maintainedincident to the, functioning of the.spark;..whereas the tube reduces or throttles the relay currentsufficiently to close. the gas. valve when said energy supply ceases andthegrid voltage drops to zero incident to cessationof the functioning ofthe spark.

The' r-ectifying energy-storing circuit is connected .across thefrequency discriminating .cir-.

'cuitmeansso: astoreceive the abstracted highfrequencyenergy vforrectification, the resistor being in parallel with; the filteringcapacitance and adapted :toautomatically discharge stored energy. to alower contr'olvoltage upon cessation of" the supply .of abstractedenergy.

A reference potential or ground .of the control system is common .to oneof said spark electrodes. a first. terminal. of the frequency-discriminating resonant. circuit, a first terminal of thefilteringcapacitance, and a first terminal of: the. relay @DOWBIRSOHICB, with therectifier as of a polarity to render the second terminal of thefiltering capacitance positive with respect to said reference potentialin response to the presence-10f. the "spark. Furthermore, thesolenoid-coil; has its first terminal connectedwith the power source atthe reference potential, and itssecond terminal connected with thecathode of: the amplifier tube, while the anode of the amplifierrtube isconnected with the second terminal. of the power source, and the grid oftheamplifiertube is connected to the second terminal of; the filteringcapacitance.

With these connections and polarities, and the spark absent, theamplifier tube current itself in' passing through the solenoid coilproducesa voltage drop biasing the cathode positive with respect to thereferencepotential thereby rendering that current self-limiting to avalue-insuflicint to allow the gas. valve to open; whereas, with thespark :present, the voltage drop appearing across the filteringcapacitance increases the current through *the amplifier tube and thesolenoid coil.:sufiiciently to. effect: opening of the gas- 15 valve.

A special safety factor characterizes this arrangement of the amplifierrelay circuit, insofar as it offers the insurance of closing the gasvalve in the event of failure of any of the components of the amplifierrelay circuit. This is because of the fact that the bias on the grid ofthe amplifier tube required for closing the gas valve is derived fromthe passage of the tube current itself through the solenoid, so that anyfailure within this amplifier relay circuit, which. would remove theaforementioned positive bias on the cathode of the amplifier tube, wouldat the same time de-energize the solenoid coil and thus allow the valveto close.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in. all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

In the drawings:

Figure 1 shows the gas burner having a spark electrode ignition systemand a solenoid-operated as supply valve, with the addition of thecontrol system capable of discriminating between the interrupted sparkproducing wave form and the uninterrupted no-spark wave form of theignition current for controlling the opening and closing of the gasvalve.

Figures 2 to 7 are voltage and current diagrams illustratingcharacteristics of spark producing current and of the no-spark current,respectively; that is Figure 2 shows a voltage wave indicating theopen-circuited voltage of the transformer secondary; Figure 3 indicatesthe uninterrupted current wave form of the no-spark current; Figure 4indicates the interrupted wave form of the spark producing current;Figure 5 is an enlarged diagram indicating the resultant voltage of ahalf-wave of the spark producing current including the high frequencycomponents; Figure 6 shows further enlarged the voltage of the highfrequency components per se; Figure '7 is a half-wave diagram taken fromFigure 4 and showing the sparkproducing current in coordination and timerelationship to the Figures 5 and 6 diagrams.

Figure 8 shows the characteristic part of the ignition circuit toillustrate the computation of the resultant voltage of the Figure 5diagram.

A gas burner ii) in Figure 1 may be of any conventional type receivingits gas supply from a gas supply pipe H through a usual nozzle [2surrounded by an annular passage it for admitting combustion air to mixwith gas from the nozzle, air and gas to mix in the short length ofmixing pipe [4 before entering the burner head proper here shown to bein the form of a ribbon burner The gas supply pipe l i has asolenoid-actuated control valve l6 as well as a hand-operated shutofifvalve ll. The valve Iii has an actuating lever It connected to a tensionsprin 18 for holding the valve closed by urging the lever lt in thedirection of arrow A1. The lever is also connected to an armature it foropening the valve It by moving the actuating lever in the direction ofarrow A2 against the tension of spring 98 when the armature is drawn inthat direction byenergization of a valve-opening solenoid 20.

8 The solenoid 20 is here shown to be energizable as from a power sourceP, for instance volts 60 cycles, through the operation of asolenoidactuated relay switch 28 which comprises a pair of relaycontacts H and 2t, an armature 20 and a solenoid coil Zil energizablefrom the power source P for moving the armature to close the contactsagainst the tension of spring 28.

The burner it together with appurtenances such as the valve ii, thevalve It with solenoidactuated lever Eri and solenoid-actuated relayswitch Zit constitute what is herein termed the burner unit A.

The burner head [5 is provided with a pair of spark electrodes indicatedat 2| and 22, electrode 2| havin a ground 23 to make it the low tensionelectrode, with electrode 22 representing the high tension electrode.These electrodes are supplied with current from an ignition transformer24 having a primary coil 25 and a secondary coil. 26 which coils arebriefly termed the primary and the secondary respectively. The primary25 having terminals 2? and 28 is shown to be supplied with the usual 110volt 60 cycle current through power line conductors 29 and 39 from lineterminals 3i and 132; the secondary 25 has terminals as and 34. Terminal3% of the secondary is connected to the high tension spark electrode 22through a conductor 35, while terminal 34 of the secondary is connectedto the low tension spark electrode 2i through conductors 36 and 3'! byway of interposed frequency .discriminating circuit means in the form ofa resonant circuit 33 which comprises an inductance 39 and a capacitance40 connected in parallel. That is, the conductor 38 atpoint 4i dividesinto a pair of branches c2 and 43, while the conductor 37 at point 44splits into a pair of branches 45 and 45.

The circuit across the transformer secondary coil 26, called thesecondary circuit, comprises the secondary coil 25, the conductor 35,the spark electrodes 2! and 22 with air gap G between them, and theconductors 3'! and 36, as well as the interposed resonant circuit 38.This secondary transformer circuit may carry either a spark producingcurrent or a "no-spark current depending upon whether the circuit isfunctioning normally or whether the electrodes have becomeshort-circuited.

; The secondary voltage of the ignition transformer 2:2 is usually ofthe order of 5090 volts across the open circuit, and the transformeritself is of th current-limiting type, that is the type delivering asecondary current not in excess of a predetermined magnitude, forinstance, of the order of 15 milliamperes, irrespective of the magnitudeof the load across the circuit, that is irrespective of whether thespark across the electrodes is functioning normally or whether theelectrodes have become short-circuited.

The transformer 24 together with the resonant circuit 33 constituteswhat is herein termed the ignition unit B. The primary and the secondarytransformer circuits including the spark electrodes 2i and 22 arehereinterrned the ignition system.

The invention is based upon the concept of utilizing, for controlpurposes, the difference between th characteristic of the sparkproducing current and that of the no-spark current.

According to this invention, the resonant circuit 38 serves forabstracting high frequency energy from the spark producing circuit, thatenergy to be utilized in producing thedesiredcontrol" efiects. Suchenergy manifests itself in the form According to another feature, theener y needed for actuating the gas valve-controlling relaymeans isconverted from A.-C. form to D.-C. form and as such is accumulated in acondenser. In other. words, the aforementioned portion of the energy inthe resonantcircuit, to be utilized. for controlling the gas valve, istransferred to and stored within the condenser. That is, the condenser,receiving increments of energy. with each ring of the resonant circuit,is enabled to hold a charge thus accumulated by a one-way conductor suchas a rectifier functionally interposed between the condenser andthesource of energy as represented by the-resonant circuit when in astate of ringing. Thus the condenser becomes gradually charged to aD.-C. voltage substantially equal to the highest peak voltage attainedby the damped sinusoidal voltage wave of the ringing. This D.-C. voltageis utilized through the relay action of a current amplifier electronictubeto hold the gas valve open while .the spark functions normally. Thatis,the D.-C. voltage is impressed upon the input electrode or grid. ofthe tube which in turn acts in proportion to such impressed voltage tovary the flow of current through the tube from an independent auxiliarypower source employed for actuating the gas valve proper. That is, theD.C. voltage from the condenser operates through the tube to hold thegas valve open only as long as the condenser remains sumciently charged,provision being made for the condenser to discharge automatically andfor the D.-C. voltage to drop to zero within a predetermined period oftime, after the supply .of energy, increments from the ringing of theresonant circuit ceases, due to spark failure. The amplifier tubecircuit is designed to shut oif the auxiliary power supply when theD.-C., grid voltage drops suificiently or becomes zero to effectautomatically the closing of the gas valve. In this way cumulativeenergy of a sequence of damped sinusoidal waves is utilized to controlthe desired functioning of the gas valve.

Summarizing, the control system comprises four functional operatingunits, namely, a gas burner unit comprising a gas burner, a pair ofignition spark electrodes for the burner, a gas control valve for theburner, and an electrically energized gas valve actuating device to holdthe valve open when energized and to close it when deenergized; (b) anignition unit comprising an ignition transformer for supplying sparkcurrent to the electrodes, and a sparkdetecting resonant circuitfunctionally coupled with the transformerin such a manner as to abstractenergy from the spark producing current; (0) a rectifying energy-storingunit comprising a rectifier for changing the abstracted A.-C. energy toD.-C. energy, a condenser for receiving rectified energy from thespark-detecting resonant circuit, and a resistor in parallel with thecondenser and dimensioned to discharge the condenser within apredetermined time after the supply of energy has ceased due to sparkfailure; (d) a relay unit comprising an electronic amplifier tube havingat least an anode, a grid, and a cathode, and controlled by the D.-C.voltage of the charge storedin the condenser so as to energize the valveactuating means or solenoid coil only while the spark is functioningnormally.

In terms of circuitsthe control systemac-H cording to "this inventionpresents itself as follows:

The ignition transformer secondarytcurrent contains high frequencycomponents only when the ignitionsparkis functioning but not when thespark is absent due to the electrodes having become short circuited.

In conjunction with the ignition circuit there are, provided frequencydiscriminating circuit means or a resonant circuit which is. frequencydiscriminating, in that it selectively abstracts energy from the highfrequency component of the spark producing current, but remainsnonresponsive to any current in which the high frequency components areabsent such as current passing through short circuited electrodes. The.abstracted energy is supplied to a. rectifying energy storing circuitwhere it is accumulated up to a predetermined voltage, from. whichcircuit the accumulated energy is automatically discharged whenever thesupplyqof energy. ceases. This predetermined voltage being amanifestation of the. stored energy is utilized in and by a relay powercircuit comprising an amplifier tube the operation :of which is governedby that voltage. That is, the voltage is impressed upon the gridofthatuam plifiertube in such a manner that the tube acts to passcurrent sufficient to actuate the valve operating means to. hold thevalve open as long as the energy supply and thereby the grid voltage arebeing maintained incident to the functioning ofthe spark; whereas thetube reduces or throttles the relay current sufficiently to close thegas valve when said energy supply ceases and the grid voltage drops tozero incident to cessation of thefunctioning of the spark.

The rectifying energy-storing circuit is connected across the frequencydiscriminating circuit means so as to receive the abstractedhighfrequency energy for rectification, the resistor being in parallelwith the filtering capacitance and adapted to automatically dischargestored energy to a lower control voltage upon cessation of the supply ofabstracted energy.

A reference potential or ground of the control systemis common to one ofsaid spark electrodes, a. first. terminal of thefrequency-discriminating resonant circuit, a first terminal of thefiltering capacitance, and a first terminal of the relay power source,with the rectifier as of a polarity to render the second terminal of thefiltering capacitance positive with respect to said reference potentialin responseto the presence of the spark. Furthermore, the solenoid coilhas its first terminal connected with the power source at the referencepotential, and its second terminal connected with the cathode of theamplifier tube, while the anode of the amplifier tube is connected withthe second terminalof the power source, and the grid of the amplifiertube is connected to the second terminal of the filtering capacitance.

With these connections and polarities, and the spark absent, theamplifier tube current itself inpassing through the solenoid coilproduces a voltage drop biasing the cathode positive with respect to thereference potential thereby rendering that current self-limiting to avalue insufiicint to allowthe gas valve to open; whereas, with the sparkpresent, the voltage drop appearing across the filtering capacitanceincreases the current through the amplifier tube and the solevalve.

A special safety factor characterizes this arrangement of the amplifierrelay circuit, insofar as it offers the insurance of closing the gasvalve in the event of failure of any of the components of the amplifierrelay circuit. This is because of the fact that the bias on the grid ofthe amplifier tube required for closing the gas valve is derived fromthe passage of the tube current itself through the solenoid, so that anyfailure within this amplifier relay circuit, which would remove theaforementioned positive bias on the cathode of the amplifier tube, wouldat the same time de-energize the solenoid coil and thus allow the valveto close.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

In the drawings:

Figure 1 shows the gas burner having a spark electrode ignition systemand a solenoid-operated gas supply valve, with the addition of thecontrol system capable of discriminating between the interrupted sparkproducing wave form and the uninterrupted no-spark wave form of theignition current for controlling the opening and closing of the gasvalve.

Figures 2 to 7 are voltage and current diagrams illustratingcharacteristics of spark producing current and of the no-spark current,respectively; that is Figure 2 shows a voltage wave indicating theopen-circuited voltage of the transformer secondary; Figure 3 indicatesthe uninterrupted current wave form of the no-spark current; Figure 4indicates the interrupted wave form of the spark producing current;Figure 5 is an enlarged diagram indicating the resultant voltage of ahalf-wave of the spark producing current including the high frequencycomponents; Figure 6 shows further enlarged the voltage of the highfrequency components per se; Figure 7 is a half-Wave diagram taken fromFigure 4 and showing the spark producing current in coordination andtime relationship to the Figures 5 and 6 diagrams.

Figure 8 shows the characteristic part of the ignition circuit toillustrate the computation of the resultant voltage of the Figure 5diagram.

A gas burner H3 in Figure 1 may be of any conventional type receivingits gas supply from a gas supply pipe I! through a usual nozzle i2surrounded by an annular passage 33 for admitting combustion air to mixwith gas from the nozzle, air and gas to mix in the short length ofmixing pipe i4 before entering the burner head proper here shown to bein the form of a ribbon burner The gas supply pipe I i has asolenoid-actuated control valve is as well as a hand-operated shutoifvalve H. The valve it has an actuating lever it connected to a tensionsprin I8 for holding the valve closed by urging the lever it in thedirection of arrow A1. The lever is also connected to an armature [9 foropening the valve l5 by moving the actuating lever in the direction ofarrow A2 against the tension of spring l8 when gization of avalve-opening solenoid 20.

'- forrner 25 is usually of the order of 5090 volts The solenoid 20 ishere shown to be energizable as from a power source P, for instancevolts 60 cycles, through the operation of a solenoidactuated relayswitch 213 which comprises a pair of relay contacts 26* and Et anarmature 20 and a solenoid coil 26 energizable from the power source Pfor moving the armature to close the contacts against the tension ofspring 26 The burner It together with appurtenances such as the valveit, the valve It with solenoidactuated lever it and solenoid-actuatedrelay switch 26 constitute what is herein termed the burner unit A.

The burner head it is provided with a pair of spark electrodes indicatedat 2| and 22, electrode 2| having a ground 23'to make it the low tensionelectrode, with electrode 22 representing the high tension electrode.These electrodes are supplied with current from an ignition transformer24 having a primary coil 25 and a secondary coil 26 which coils arebriefly termed the primary and the secondary respectively. The primary25 hav-- ing terminals 2? and 28 is shown to be supplied with the usual110 volt 60 cycle current through power line conductors 29 and 3% fromline terminals 3i and 32; the secondary it has terminals 33' and 3%.Terminal 33 of the secondary is connected to the high tension sparkelectrode 22 through a conductor 35, while terminal 34% of the secondaryis connected to the low. tension spark electrode 2i through conductorsE5 and 37 by way of interposed frequency discriminating circuit means inthe form of a resonant circuit 33 which comprises an inductance 39 and acapacitance 49 connected in parallel. That is, the conductor 33 at pointGI divides into a pair of branches l2 and while the conductor til atpoint t4 splits into a pair of branches 45 and 46.

The circuit across the transformer secondary coil as, called thesecondary circuit, comprises the secondary coil 25, the conductor 35,the spark electrodes 2] and 22 with air gapG between them, and theconductors 3'! and as Well as the interposed resonant circuit 33.transformer circuit may carry eithera spark producing current or ano-spark current depending upon whether the circuit is functioningnormally or whether the electrodes have become short-circuited.

The secondary voltage of the ignition transacross the open circuit, andthe transformer itself is of th current-limiting type, that is thetypedelivering a secondary current not in excess of a predeterminedmagnitude, for instance, of the order of 15 milliamp-eres, irrespectiveof the magnitude of the load across the circuit, that is irrespective ofwhether the spark across the elec-' trodes is functioning normally orWhether the electrodes have become short-circuited.

The transformer 24 together with the resonant circuit 38 constitutesWhat is herein termed theignition unit 13. The primary and the secondarytransformer circuits including the spark electrodes 2! and 22 are hereintermed the ignition system.

The invention is based upon the concept of utilizing, for controlpurposes, the difference between ergy from the spark producing circuit,that energy to be utilized in producing the desired control effects Suchenergy manifests itself inthe form This secondary 9 of a dampedsinusoidal voltage wave across the terminals 4! and i l of the resonancecircuit. The characteristics and functions of a resonant circuit as suchare known. Suflice it to say at this point that the high frequencyenergy components of the spark producing current, as represented by thedamned sinusoidal waves manifest themselves in the ringing of theresonant circuit as and when the rapid increases and the rapid decreasesoccur in the interrupted wav form of the spark producing current.Instead of allowing that .en-

ergy to dissipate itself entirely within the resonant circuit 38, thisinvention provides an energyconvertingand energy-storing circuit acrossthe terminals of the resonant circuit, namely across the terminal 34 andground 23 which is the same as ground 59. This energy-converting, andstoring circuit serves to convert a portion of the high frequency energyto D.-C. energy and for continuously storing such converted energy. Thestored energy is utilized for holding the gas valve i6 open only as longas such energy is supplied from the resonant circuit, the valve to closewhen such energy ceases to be supplied due to failure of the spark aswhen the electrodes 2| and 22 have become short-circuited.

The manner-in which the energy supplied by the resonant cir uitiitisutilized to effect the desired control will be explained in greaterdetail below in conjunction with a discussion of the Figures 2 to 7diagrams illustrating the difference in the characteristics of the sparkproducing current and of the no-spark current respectively.

The energy converting and storing circuit oomprises a rectifier hereshown in the form of a halfwave rectifying electronic tube iii termedhalfwave rectifier having an anode A8 with terminal T31 and a cathode 48with terminal T4, and a condenser 59 with a resistor R connected inpara1- lel therewith, the resistor having terminals T1 and T2. Theresistor R functions as a lay-pass for the condenser 49 to automaticallydischarge the condenser within a predetermined time after the supply ofenergy ceases, such function and its significance to be explainedfurtherbelow.

A conductor 5i! leads from terminal Bd of the transformer secondary tothe rectifier anode 43 The cathode 43 of the rectifier has a terminal T;from which a conductor 52 leads to a branch point 53 for a pair ofconductors 54 and 55, branch 54 leading to terminal T1 of resistor R andbranch 55 leading to the positiv plate Mi of condenser 49. The parallelconnection of resist-or R with condenser 49 is completed by a pair ofconductors 5t and 51 leading respectively from resistor terminal T2 andfrom the negativ plate 49* of condenser dii toa juncture point 5%connected to a ground 59. In this way the energy converting and storingcircuit is connected across or in parallel with the resonant circuit533. Th rectifier tube d3 constitutes together with the condenser dtiand with the resistor R an energy storing unit C indicated as such bythe dot-and-dash lino frame around it.

The condenser 49 and the resistor R are so dimensioned with respect toeach other that the resistor permits just enough leakage of energytherethrough to allow the condenser to be charged to the peak voltage ofthe damped sinusoidal energy waves, yet so that the condenser willdischarge byway of the resistor within :a predetermined length of timeafter the supply of high frequency energy to the condenser :has ceasedin case the spark electrodes 2| and 22 have become short-circuited.

As longas high frequency energy is supplied from the ignition system tothe energy storing circuit, that circuit manifests its charge by a D.-C.voltage at the output or cathode terminal T4 of rectifier it, whichvoltage drops to zero wh-enthe supply of high frequency energy ceases.This Dl-C. voltage a criterion of the functioning of the sparkelectrodes 2! and 22, and is utilized to furnish control. impulsesforclosing the gas valve i6 whenever this voltage disappears and to keepthe valve open as long as the voltage is maintained.

A relay circuit is provided for actuating the gas valve !5 with. anelectronic tube till controlling th current in that circuit. Theelectronic tube E50 has an anode ti with terminal di a cathode '52 withterminal 62 and a control grid 63, which tube is herein also identifiedas a relay unit D indicated as such by a dot-and-dash line frame aroundit. A conductor 64 leads from terminal T4 of rectifier cathode 48 tocontrol grid 63 for impressing upon the grid the D.-C. voltage ofstorage condenser 59.

The amplifier tube lid is designed to pass there- .through a relaycurrent of sufficient magnitude to leading from terminal 28011 powerline 30 to anode terminal di of tube til, the tube 60; a conductor E6leading from cathode terminal: 8'12 of tube 60 to a terminal fill ofsolenoid coil 26% the solenoid coil 26 a conductor 6% leading from theother terminal 69 of solenoid coil'2il to a point 10, a conductor Hleading. from pointu'Hi to a point 12 connected to ground 59, and aconductor 13 1eaoling from point 12 to a terminal hi on power line 29.

The solenoid w when energized draws the armature 20 thus closingcontacts 2t and 29 of relay switch 2th against the tension of a spring20 thus closing a secondary relay circuit which comprises a conductor 76leading from anode terminal Gl connecting with power line 3!) toterminal T5 of stationary switch' contact 20 relay switch contacts 20and 26, a conductor 11 leading from terminal T6 of movable switchcontact 20 to terminal ilil of solenoid coil 20, solenoid coil 20 and aconductor 18 leading from terminal 243 to point it connecting with thepower line 29.

Now follows the description and the discussion of the Figures 2 to '7diagrams, so that the manner in. which the abstracted high frequency energy is utilized may be more fully understood.

The wave shown in the Figure 2 diagram indicates the open-circuitedvoltage Vof the transformer secondary and as a function of time, and byestablishing the points of zero voltage M, N; O furnishes the timecycle. as a basis of comparison of the uninterrupted waveform of theno-spark current of Figure 3 with the interrupted Wave form of the sparkproducing current in Figure l. Corresponding points ofzero voltage areindicated at M1, N1, 01in Figure 3, andv at MalN .Oz in-Figure Thevoltage wave of Figure ziscomposed of a series of half-waves indicatedby: the lengths H on the abscissa, that is the ldistanceI-I betweenanytwo zero points.

For the purpose of comparison the lengths H are also indicated inFigures 3 and l.

The Figure 3 diagram illustrates the uninterrupted smooth wave form ofthe no-spark current I composed of half-waves H the actual voltage ofwhich need not be that of Figure 2, the half-waves being defined by thepoints of zero voltage M1, N1, 01.

In the interrupted wave form of the spark producing current in Figure 4a half-Wave of the length H comprises characteristically a sparkproducing current 11. The current 121 extends over a length H1 on theabscissa beginning a distance S1 from the point M2 of zero voltage andending a distance 52 from the point N2 of zero voltage. This current I1comprises (see also in Figure 7) an initial steeply rising portion :01defined by points a and b; a major inter" mediate portion 322 of shallowconvexity and defined. by points b and c with a maximum value Imax, anda steeply falling portion n defined by points and :2. Measured upon thealbscissa the portions 191, p3 of current 11 are defined by thehorizontal distances d1, d2, d3. That is to say, the spark and therewiththe current starts only after the open circuit voltage has reached avalue V1 (see Figure sufiicient to break down the spark gap G. Startinat point a the current rises rapidly to point 1) through a time intervaldefined by the distance :11 to a value I1 which is nearly that of themaximum value Imax because of the current limiting characteristic of thetransformer 26. The current is maintained along the shallow convexportion along the line P2 from point 1) to point "0 through a timeinterval 112 producing and maintaining a spark.

At point 0 when the voltage reaches a value Ve (see Figure 5)insufiicient to maintain the spark, the spark disappears at that voltageas the current drops rapidly from a value Ie to zero from point e topoint "d along the line P3 through a time interval d3. The concurrentspark load voltage Vs is indicated in Figure 5 between points e and "1"corresponding to points 1) and "c in Figure 7, by a line of shallowconvexity with a maximum voltage vmax.

The initial rapidly rising portion P1 of the current provides within thetransformer secondary circuit a high frequency energy componentmanifesting itself in the form of a damped sinusoidal voltage wave W1shown per se in Figure 6 to extend through a time interval (is. Thishigh frequency wave has a starting point g which corresponds to point ein Figure 5 and to point b in Figure '7. Similarly, the rapidly fallingterminal portion 703 of the current provides within the transformersecondary circuit a high frequency energy component manifesting itselfin the form of a damped sinusoidal voltage wave We (see Figure 6)extending through a time interval d5. This high frequency wave has astarting point h which corresponds to point I in Figure 5 and to point din Figure 7. The absolute maximum initial voltages of the high frequencywaves W1 and Wt are indicated at Fina and F'mix respectively.

The high frequency waves W1 and Wt of Figure 6 appear as waves W1 and Wtembodied in the Figure 5 diagram of the spark producing voltagehalf-Wave Vs, so that the voltage indicated by the full line in Figure5- is the resultant voltage appearing across the spark electrodes 2! and22. The resultant spark producing voltage due to the appearance of thehigh frequency waves is computable as Vs=e-e1 (see Figure 8 auxiliarywiring diagram), hence the peaks of waves W1 and Wt point in oppositedirections to that of waves W1 and Wt.

Operation When the ignition system as such is function ing normally,that is when a spark appears across the electrodes 2| and 22, such sparkis being maintained by the interrupted current wave of Figures 4 and '7together with the spark producing voltage Vs of Figure 5 includingthe'high frequency components W1 and Wt. Such spark producing current isdelivered by the secondary 26 of transformer 24 through the intermediaryof the resonant circuit 38, the transformer primary 25 being suppliedwith the usual 110 volt cycle alternating current indicated by powersource P and line terminals 3| and 32.

A portion of the high frequency energy represented by the voltage wavesW1 and Wt appearing across points 34 and 44 of the resonant circuit isabsorbed and stored by the energy converting and storing unit Cconnected across resonant circuit Sllat points 3 3 and 44 by way'ofgrounds 23 and 59. That is to say, whenever the instantaneous value ofthe high frequency voltage Waves W1 and Vii: as measured at the anode 48of rectiiier 48 becomes more positive than the cathode 48 of rectifier48, then current flows through the rectifier 43 into the condenser 49raising the difference of potential or voltage between condenser plates49 and 49*. However, when the anode it becomes more negative than thecathode 48 any flow of current through the rectifier is blocked. Thus aportion of the high frequency energy is rectified.

A portion of the condenser charge leaks out continuously by Way of thedischarge resistor R in parallel with the condenser 49. However, theenergy thus leaking out from the condenser through the dischargeresistor R is small as compared with the rectified energy suppliedthereto, so that the condenser attains and holds a l 1 charge ofsuflicient voltage to be utilized in main taining and sustaining acontrol efiect whereby the gas valve IE5 is kept open. This'controleffect is attained by the condenser voltage appearing at point T4 beingimpressed upon the control grid E3 of electronic tube til. The tubeoperates so that it passes relay current in proportion to the magnitudeof the impressed voltage, that is, the more positive the grid becomes,the larger is the current passed by the tube. The grid voltage thusimpressed is sufiicient to pass relay current from line terminal 28 toterminal 14 to energize solenoid coil 28 drawing armature 25- to closecontacts 26' and 25 against the tension of spring 23. The closing ofthese contacts in turn closes a circuit from supply terminal 28toterminal 14 to energize the solenoid coil 26 for drawing in thearmature 59 against the tension of spring it to hold open the gas valveis. Consequently, as long as the spark functions normally across sparkelectrodes 2| and 22 the gas valve I6 is maintained open.

If the spark is absent, then there is also absent the phenomenon of thehigh frequency voltage waves W1 and Wt', so that rectified energy is nolonger supplied to the condenser it. In such case the condenserdischarges through discharge resistor R. Concurrently the condenservoltage and thus the voltage on control grid 63 drops sufiiciently tochoke oil the relay current hich has so far been passing through thetube 60;

:z-acmccc "This causes solenoidcoil Ell to be deenergized cult means orresonant circuit 38, the terminal 69 of solenoid coil 26*, the junctionpoint 58 between'the capacitance at and resistor R, and the lineterminal SE of power source P, all are connected together at what isherein termed the reference potential.

Furthermore, the polarity of the rectifier :28 is such that the junctionpoint 53 between the capacitance ill and resistor R is rendered positivewith respect to the reference potential in response to the presence ofthe spark.

Thus, in the absence of the spark, the voltage across the filteringcapacitance t9 drops to substantially zero placing grid 53 of amplifiertube fit substantially at the reference potential. Concurrently acurrent will pass from terminal 223 of power source P through theamplifier tube til and through the solenoid coil 23 to terminal ll]which is at the reference potential. This current sets up a voltage dropacross the solenoid coil 26, which places the cathode 62 of amplifiertube 59 at a positive potential with respect to the reference potential.

This means that, with the grid 63 at reference potential and the cathodepositive with respect to the reference potential, the grid then isactually negative with respect t the cathode, hence as the cathodebecomes more positive with respect to the reference potential thecurrent diminishes accordingly. That is to say, the characteristics ofthe amplifier tube and of the solenoid are so coordinated that in theabsence of an adequate control voltage at terminal T4 (in the absence ofthe spark), the current through amplifier tube 58 and solenoid fil isself-limiting and thus maintains itself at a value insufficient toeffect the opening of the gas valve. This amplifier relay circuit(between power terminals 28 and 70) embodies a safety factor insofar asit insures the closing of the gas valve in the event of failure of anyof the components of the amplifier relay circuit. This is due to thefact that the bias on the grid 53 required for closing the gas valve isderived from the passage of the tube current itself through the solenoid283 so that any failure within this amplifier relay circuit, which wouldremove the aforementioned positive bias on the cathode 52, would at thesame time lie-energize the solenoid coil 26 and thus allow the gas valveto close.

On the other hand, in the presence of the spark, with a sufficientlylarge voltage drop ap peering across the filtering capacitance is whenthe grid 53 of amplifier tube it becomes biased to a higher positivepotential with respect to the reference potential, such condition willincrease the current passing through amplifier tube 55 and solenoid coil28 sufiiciently to effect opening of the gas valve. In other words, asthe grid 63 becomes more positive, the current through the tube 53 andthrough solenoid coil fill increases acccrdingly. The result is thatwhen the grid 83 has attained a suficiently high positive potential withrespect to the reference potential, then the tube current will haveincreased to a value sufiicient to effect opening of the gas valve.

Since this invention is based broadly upon the conceptrof utilizingthe'high frequency'components of the spark producing current for controlpurposes, I it lies within the scope of the invention that thehighfrequency energy abstracting means can be embodied in means other thanthe specific parallel resonant circuit 38 shown.

" For example, instead of placing that resonant circuit in the lowtension side of the transformer secondary circuit as shown in the Figurel embodiment, this resonant circuit may for example also be placed inthe high tension side of the secondary, orin the low tension side of theprimary, or in any other place in the transformer circuit where it iselectrically coupled to the high frequency components of the sparkproducing current. Furthermore, within the scope of this invention, theenergy abstracting means themselves may take forms other than that ofthe parallel resonant circuit shown, for instance the form of a seriesresonant circuit, or of a circuit from a group comprising all high-passcircuits so-called because they respond to high frequency currents abovea predetermined minimum frequency.

What is claimed is:

1. In combination with a gas burner having a gas valve to open and closethe gas supply to the burner, electrically energizable means foroperating the valve, the burner having a pair of ignition sparkelectrodes and having electrical means to produce sparking between theelectrodes; a control system utilizing the absence and presence of highfrequency components of the spark producing current in controlling thefuel supply to the burner to effect fuel shutoff in the absence of thespark, and comprising frequency discriminating circuit means operativelyassociated with the spark-producing circuit for selectively ab- 0stracting energy from the high-frequency comfrequency energy forrectification and comprising a rectifier, a filtering capacitance inseries with the rectifier for storing a quantity of rectified energy ata predetermined maximum control voltage, and a resistor in parallel withthe filtering capacitance and adapted to automatically discharge storedenergy to a lower control voltage upon cessation of the supply ofabstracted rectified energy, a relay power circuit comprising a powersource, an amplifier tube having at least an anode, a grid and acathode, a solenoid coil adapted to effect the opening of the gas valvewhen energized while allowing the gas valve to close when de-enermzed,connections applying a common reference potential to one of said sparkelectrodes, a first terminal of said frequency-disoriminating circuitmeans, a first terminal of said filtering capacitance, and a firstterminal of said relay power source, with the polarity of said rectifierbeing such as to render the second terminal of said filteringcapacitance positive with respect to said reference potential inresponse to the presence of the spark, said solenoid coil having itsfirst terminal connected with said power source at said referencepotential and its second terminal connected with the cathode of theamplifier tube, the anode of said amplifier tube being connected withthe second terminal of the power source, and the grid of said amplifiertube being connected to the second terminal of said filteringcapacitance, whereby with the spark absent the amplifier tube' currentitself in passing through the solenoid coil produces a voltage dropbiasing the cathode positive with respect to the reference potentialthereby rendering that current self-limiting to a value insuflicient toefiect the opening of the gas valve whereas with the spark present thevoltage drop appearing across the filtering capacitance increases thecurrent through said tube and solenoid sufiiciently to effect theopening of the gas valve.

2. The system according to claim 1, in which thefrequency-discriminating circuit means comprises an inductance and acondenser connected in parallel to constitute a resonant circuit, saidcircuit means being interposed between a spark electrode at saidreference potential and a terminal of said spark producing electricalmeans.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,755,390 Fischer Apr. 22, 1930 2,154,041 Gille Apr. 11, 19392,196,442 Maynard Apr. 9, 1940 2,406,185 Aubert Aug. 20, 1946

